staging/lustre/osc: Do not use lprocfs_write_helper in sysfs store methods

sysfs store methods provide us with a kernel buffer already, but
lprocfs_write_helper is expecting a user buffer.
Replace lprocfs_write_helper with kstrto[u]int() calls instead in
contention_seconds_store() and lockless_truncate_store()

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>